有关于HibernateSessionFactory问题

大家都知道SessionFactory是重量级封装，创建一个SessionFactory是非常耗资源的。所以，一般而言，我们都会写一个静态的方法来获得SessionFactory，以下代码是myEclipse自动生成的代码。

import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.cfg.Configuration;

/**
* Configures and provides access to Hibernate sessions, tied to the
* current thread of execution. Follows the Thread Local Session
* pattern, see {@link http://hibernate.org/42.html}.
*/
public class HibernateSessionFactory {

/**
* Location of hibernate.cfg.xml file.
* NOTICE: Location should be on the classpath as Hibernate uses
* #resourceAsStream style lookup for its configuration file. That
* is place the config file in a Java package - the default location
* is the default Java package.<br/><br/>
* Examples: <br/>
* <code>CONFIG_FILE_LOCATION = "/hibernate.conf.xml".
* CONFIG_FILE_LOCATION = "/com/foo/bar/myhiberstuff.conf.xml".</code>
*/
private static String CONFIG_FILE_LOCATION = "/hibernate.cfg.xml";

/** Holds a single instance of Session */
private static final ThreadLocal threadLocal = new ThreadLocal();

/** The single instance of hibernate configuration */
private static final Configuration cfg = new Configuration();

/** The single instance of hibernate SessionFactory */
private static org.hibernate.SessionFactory sessionFactory;

/**
* Returns the ThreadLocal Session instance. Lazy initialize
* the <code>SessionFactory</code> if needed.
*
* @return Session
* @throws HibernateException
*/
public static Session currentSession() throws HibernateException {
Session session = (Session) threadLocal.get();

if (session == null || !session.isOpen()) {
if (sessionFactory == null) {
try {
cfg.configure(CONFIG_FILE_LOCATION);
sessionFactory = cfg.buildSessionFactory();
} catch (Exception e) {
System.err
.println("%%%% Error Creating SessionFactory %%%%");
e.printStackTrace();
}
}
session = (sessionFactory != null) ? sessionFactory.openSession()
: null;
threadLocal.set(session);
}

return session;
}

/**
* Close the single hibernate session instance.
*
* @throws HibernateException
*/
public static void closeSession() throws HibernateException {
Session session = (Session) threadLocal.get();
threadLocal.set(null);

if (session != null) {
session.close();
}
}

/**
* Default constructor.
*/
private HibernateSessionFactory() {
}

}

这样就大大方便了我们的操作。比如：
Session session = HibernateSessionFactory.currentSession() ; //获取Session对象
Transaction tx = session.beginTransaction(); //事务开始
//进行一些操作
session.save(obj);
tx.commit(); //关闭事务
可要注意，之前我们获取了一个session对象，现问：
是不是每调用一次HibernateSessionFactory.currentSession() ;
都要对应着HibernateSessionFactory.closeSession();

问题来啦，SessionFactory是非常耗资源的，如果关闭的话，那岂不是性能非常的低下。如果不关闭的话，好像又有点不妥。
如果我只获取而不关闭的话，会怎样？

初学hibernate,望大虾解答。

closeSession();应该不是close HibernateSessionFactory 吧

你可以写个HibernateUtil,这样子就可以关了
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class HibernateUtil {

private static Log log=LogFactory.getLog(HibernateUtil.class);

private static final SessionFactory sessionFactory;

static {
try{
sessionFactory=new Configuration().configure().buildSessionFactory();
} catch (Throwable ex) {
log.error("Initial SessionFactory creation failed.",ex);
throw new ExceptionInInitializerError(ex);
}
}

public static final ThreadLocal session=new ThreadLocal();

public static Session currentSession() throws HibernateException {
Session s=(Session)session.get();
//Open a new Session, if this Thread has none yet
if (s==null) {
s=sessionFactory.openSession();
session.set(s);
}
return s;
}

public static void closeSession() throws HibernateException {
Session s=(Session) session.get();
session.set(null);
if (s !=null)
s.close();
}

}